text: # Copyright 2017 New Vector Ltd
  # Copyright 2019 The Matrix.org Foundation C.I.C.
  #
  # Licensed under the Apache License, Version 2.0 (the "License");
  # you may not use this file except in compliance with the License.
  # You may obtain a copy of the License at
  #
  #     http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS,
  # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  # See the License for the specific language governing permissions and
  # limitations under the License.
  
  import inspect
  import logging
  from typing import (
      TYPE_CHECKING,
      Any,
      Awaitable,
      Callable,
      Collection,
      Dict,
      List,
      Optional,
      Tuple,
      Union,
  )
  
  from synapse.api.errors import Codes
  from synapse.rest.media.v1._base import FileInfo
  from synapse.rest.media.v1.media_storage import ReadableFileWrapper
  from synapse.spam_checker_api import RegistrationBehaviour
  from synapse.types import RoomAlias, UserProfile
  from synapse.util.async_helpers import delay_cancellation, maybe_awaitable
  from synapse.util.metrics import Measure
  
  if TYPE_CHECKING:
      import synapse.events
      import synapse.server
  
  logger = logging.getLogger(__name__)
  
  CHECK_EVENT_FOR_SPAM_CALLBACK = Callable[
      ["synapse.events.EventBase"],
      Awaitable[
          Union[
              str,
              Codes,
              # Highly experimental, not officially part of the spamchecker API, may
              # disappear without warning depending on the results of ongoing
              # experiments.
              # Use this to return additional information as part of an error.
              Tuple[Codes, Dict],
              # Deprecated
              bool,
          ]
      ],
  ]
  SHOULD_DROP_FEDERATED_EVENT_CALLBACK = Callable[
      ["synapse.events.EventBase"],
      Awaitable[Union[bool, str]],
  ]
  USER_MAY_JOIN_ROOM_CALLBACK = Callable[[str, str, bool], Awaitable[bool]]
  USER_MAY_INVITE_CALLBACK = Callable[[str, str, str], Awaitable[bool]]
  USER_MAY_SEND_3PID_INVITE_CALLBACK = Callable[[str, str, str, str], Awaitable[bool]]
  USER_MAY_CREATE_ROOM_CALLBACK = Callable[[str], Awaitable[bool]]
  USER_MAY_CREATE_ROOM_ALIAS_CALLBACK = Callable[[str, RoomAlias], Awaitable[bool]]
  USER_MAY_PUBLISH_ROOM_CALLBACK = Callable[[str, str], Awaitable[bool]]
  CHECK_USERNAME_FOR_SPAM_CALLBACK = Callable[[UserProfile], Awaitable[bool]]
  LEGACY_CHECK_REGISTRATION_FOR_SPAM_CALLBACK = Callable[
      [
          Optional[dict],
          Optional[str],
          Collection[Tuple[str, str]],
      ],
      Awaitable[RegistrationBehaviour],
  ]
  CHECK_REGISTRATION_FOR_SPAM_CALLBACK = Callable[
      [
          Optional[dict],
          Optional[str],
          Collection[Tuple[str, str]],
          Optional[str],
      ],
      Awaitable[RegistrationBehaviour],
  ]
  CHECK_MEDIA_FILE_FOR_SPAM_CALLBACK = Callable[
      [ReadableFileWrapper, FileInfo],
      Awaitable[bool],
  ]
  
  
  def load_legacy_spam_checkers(hs: "synapse.server.HomeServer") -> None:
      """Wrapper that loads spam checkers configured using the old configuration, and
      registers the spam checker hooks they implement.
      """
      spam_checkers: List[Any] = []
      api = hs.get_module_api()
      for module, config in hs.config.spamchecker.spam_checkers:
          # Older spam checkers don't accept the `api` argument, so we
          # try and detect support.
          spam_args = inspect.getfullargspec(module)
          if "api" in spam_args.args:
              spam_checkers.append(module(config=config, api=api))
          else:
              spam_checkers.append(module(config=config))
  
      # The known spam checker hooks. If a spam checker module implements a method
      # which name appears in this set, we'll want to register it.
      spam_checker_methods = {
          "check_event_for_spam",
          "user_may_invite",
          "user_may_create_room",
          "user_may_create_room_alias",
          "user_may_publish_room",
          "check_username_for_spam",
          "check_registration_for_spam",
          "check_media_file_for_spam",
      }
  
      for spam_checker in spam_checkers:
          # Methods on legacy spam checkers might not be async, so we wrap them around a
          # wrapper that will call maybe_awaitable on the result.
          def async_wrapper(f: Optional[Callable]) -> Optional[Callable[..., Awaitable]]:
              # f might be None if the callback isn't implemented by the module. In this
              # case we don't want to register a callback at all so we return None.
              if f is None:
                  return None
  
              wrapped_func = f
  
              if f.__name__ == "check_registration_for_spam":
                  checker_args = inspect.signature(f)
                  if len(checker_args.parameters) == 3:
                      # Backwards compatibility; some modules might implement a hook that
                      # doesn't expect a 4th argument. In this case, wrap it in a function
                      # that gives it only 3 arguments and drops the auth_provider_id on
                      # the floor.
                      def wrapper(
                          email_threepid: Optional[dict],
                          username: Optional[str],
                          request_info: Collection[Tuple[str, str]],
                          auth_provider_id: Optional[str],
                      ) -> Union[Awaitable[RegistrationBehaviour], RegistrationBehaviour]:
                          # Assertion required because mypy can't prove we won't
                          # change `f` back to `None`. See
                          # https://mypy.readthedocs.io/en/latest/common_issues.html#narrowing-and-inner-functions
                          assert f is not None
  
                          return f(
                              email_threepid,
                              username,
                              request_info,
                          )
  
                      wrapped_func = wrapper
                  elif len(checker_args.parameters) != 4:
                      raise RuntimeError(
                          "Bad signature for callback check_registration_for_spam",
                      )
  
              def run(*args: Any, **kwargs: Any) -> Awaitable:
                  # Assertion required because mypy can't prove we won't change `f`
                  # back to `None`. See
                  # https://mypy.readthedocs.io/en/latest/common_issues.html#narrowing-and-inner-functions
                  assert wrapped_func is not None
  
                  return maybe_awaitable(wrapped_func(*args, **kwargs))
  
              return run
  
          # Register the hooks through the module API.
          hooks = {
              hook: async_wrapper(getattr(spam_checker, hook, None))
              for hook in spam_checker_methods
          }
  
          api.register_spam_checker_callbacks(**hooks)
  
  
  class SpamChecker:
      NOT_SPAM = "NOT_SPAM"
  
      def __init__(self, hs: "synapse.server.HomeServer") -> None:
          self.hs = hs
          self.clock = hs.get_clock()
  
          self._check_event_for_spam_callbacks: List[CHECK_EVENT_FOR_SPAM_CALLBACK] = []
          self._should_drop_federated_event_callbacks: List[
              SHOULD_DROP_FEDERATED_EVENT_CALLBACK
          ] = []
          self._user_may_join_room_callbacks: List[USER_MAY_JOIN_ROOM_CALLBACK] = []
          self._user_may_invite_callbacks: List[USER_MAY_INVITE_CALLBACK] = []
          self._user_may_send_3pid_invite_callbacks: List[
              USER_MAY_SEND_3PID_INVITE_CALLBACK
          ] = []
          self._user_may_create_room_callbacks: List[USER_MAY_CREATE_ROOM_CALLBACK] = []
          self._user_may_create_room_alias_callbacks: List[
              USER_MAY_CREATE_ROOM_ALIAS_CALLBACK
          ] = []
          self._user_may_publish_room_callbacks: List[USER_MAY_PUBLISH_ROOM_CALLBACK] = []
          self._check_username_for_spam_callbacks: List[
              CHECK_USERNAME_FOR_SPAM_CALLBACK
          ] = []
          self._check_registration_for_spam_callbacks: List[
              CHECK_REGISTRATION_FOR_SPAM_CALLBACK
          ] = []
          self._check_media_file_for_spam_callbacks: List[
              CHECK_MEDIA_FILE_FOR_SPAM_CALLBACK
          ] = []
  
      def register_callbacks(
          self,
          check_event_for_spam: Optional[CHECK_EVENT_FOR_SPAM_CALLBACK] = None,
          should_drop_federated_event: Optional[
              SHOULD_DROP_FEDERATED_EVENT_CALLBACK
          ] = None,
          user_may_join_room: Optional[USER_MAY_JOIN_ROOM_CALLBACK] = None,
          user_may_invite: Optional[USER_MAY_INVITE_CALLBACK] = None,
          user_may_send_3pid_invite: Optional[USER_MAY_SEND_3PID_INVITE_CALLBACK] = None,
          user_may_create_room: Optional[USER_MAY_CREATE_ROOM_CALLBACK] = None,
          user_may_create_room_alias: Optional[
              USER_MAY_CREATE_ROOM_ALIAS_CALLBACK
          ] = None,
          user_may_publish_room: Optional[USER_MAY_PUBLISH_ROOM_CALLBACK] = None,
          check_username_for_spam: Optional[CHECK_USERNAME_FOR_SPAM_CALLBACK] = None,
          check_registration_for_spam: Optional[
              CHECK_REGISTRATION_FOR_SPAM_CALLBACK
          ] = None,
          check_media_file_for_spam: Optional[CHECK_MEDIA_FILE_FOR_SPAM_CALLBACK] = None,
      ) -> None:
          """Register callbacks from module for each hook."""
          if check_event_for_spam is not None:
              self._check_event_for_spam_callbacks.append(check_event_for_spam)
  
          if should_drop_federated_event is not None:
              self._should_drop_federated_event_callbacks.append(
                  should_drop_federated_event
              )
  
          if user_may_join_room is not None:
              self._user_may_join_room_callbacks.append(user_may_join_room)
  
          if user_may_invite is not None:
              self._user_may_invite_callbacks.append(user_may_invite)
  
          if user_may_send_3pid_invite is not None:
              self._user_may_send_3pid_invite_callbacks.append(
                  user_may_send_3pid_invite,
              )
  
          if user_may_create_room is not None:
              self._user_may_create_room_callbacks.append(user_may_create_room)
  
          if user_may_create_room_alias is not None:
              self._user_may_create_room_alias_callbacks.append(
                  user_may_create_room_alias,
              )
  
          if user_may_publish_room is not None:
              self._user_may_publish_room_callbacks.append(user_may_publish_room)
  
          if check_username_for_spam is not None:
              self._check_username_for_spam_callbacks.append(check_username_for_spam)
  
          if check_registration_for_spam is not None:
              self._check_registration_for_spam_callbacks.append(
                  check_registration_for_spam,
              )
  
          if check_media_file_for_spam is not None:
              self._check_media_file_for_spam_callbacks.append(check_media_file_for_spam)
  
      async def check_event_for_spam(
          self, event: "synapse.events.EventBase"
      ) -> Union[Tuple[Codes, Dict], str]:
          """Checks if a given event is considered "spammy" by this server.
  
          If the server considers an event spammy, then it will be rejected if
          sent by a local user. If it is sent by a user on another server, the
          event is soft-failed.
  
          Args:
              event: the event to be checked
  
          Returns:
              - `NOT_SPAM` if the event is considered good (non-spammy) and should be let
                  through. Other spamcheck filters may still reject it.
              - A `Code` if the event is considered spammy and is rejected with a specific
                  error message/code.
              - A string that isn't `NOT_SPAM` if the event is considered spammy and the
                  string should be used as the client-facing error message. This usage is
                  generally discouraged as it doesn't support internationalization.
          """
          for callback in self._check_event_for_spam_callbacks:
              with Measure(
                  self.clock, "{}.{}".format(callback.__module__, callback.__qualname__)
              ):
                  res = await delay_cancellation(callback(event))
                  if res is False or res == self.NOT_SPAM:
                      # This spam-checker accepts the event.
                      # Other spam-checkers may reject it, though.
                      continue
                  elif res is True:
                      # This spam-checker rejects the event with deprecated
                      # return value `True`
                      return Codes.FORBIDDEN
                  elif not isinstance(res, str):
                      # mypy complains that we can't reach this code because of the
                      # return type in CHECK_EVENT_FOR_SPAM_CALLBACK, but we don't know
                      # for sure that the module actually returns it.
                      logger.warning(
                          "Module returned invalid value, rejecting message as spam"
                      )
                      res = "This message has been rejected as probable spam"
                  else:
                      # The module rejected the event either with a `Codes`
                      # or some other `str`. In either case, we stop here.
                      pass
  
                  return res
  
          # No spam-checker has rejected the event, let it pass.
          return self.NOT_SPAM
  
      async def should_drop_federated_event(
          self, event: "synapse.events.EventBase"
      ) -> Union[bool, str]:
          """Checks if a given federated event is considered "spammy" by this
          server.
  
          If the server considers an event spammy, it will be silently dropped,
          and in doing so will split-brain our view of the room's DAG.
  
          Args:
              event: the event to be checked
  
          Returns:
              True if the event should be silently dropped
          """
          for callback in self._should_drop_federated_event_callbacks:
              with Measure(
                  self.clock, "{}.{}".format(callback.__module__, callback.__qualname__)
              ):
                  res: Union[bool, str] = await delay_cancellation(callback(event))
              if res:
                  return res
  
          return False
  
      async def user_may_join_room(
          self, user_id: str, room_id: str, is_invited: bool
      ) -> bool:
          """Checks if a given users is allowed to join a room.
          Not called when a user creates a room.
  
          Args:
              userid: The ID of the user wanting to join the room
              room_id: The ID of the room the user wants to join
              is_invited: Whether the user is invited into the room
  
          Returns:
              Whether the user may join the room
          """
          for callback in self._user_may_join_room_callbacks:
              with Measure(
                  self.clock, "{}.{}".format(callback.__module__, callback.__qualname__)
              ):
                  may_join_room = await delay_cancellation(
                      callback(user_id, room_id, is_invited)
                  )
              if may_join_room is False:
                  return False
  
          return True
  
      async def user_may_invite(
          self, inviter_userid: str, invitee_userid: str, room_id: str
      ) -> bool:
          """Checks if a given user may send an invite
  
          If this method returns false, the invite will be rejected.
  
          Args:
              inviter_userid: The user ID of the sender of the invitation
              invitee_userid: The user ID targeted in the invitation
              room_id: The room ID
  
          Returns:
              True if the user may send an invite, otherwise False
          """
          for callback in self._user_may_invite_callbacks:
              with Measure(
                  self.clock, "{}.{}".format(callback.__module__, callback.__qualname__)
              ):
                  may_invite = await delay_cancellation(
                      callback(inviter_userid, invitee_userid, room_id)
                  )
              if may_invite is False:
                  return False
  
          return True
  
      async def user_may_send_3pid_invite(
          self, inviter_userid: str, medium: str, address: str, room_id: str
      ) -> bool:
          """Checks if a given user may invite a given threepid into the room
  
          If this method returns false, the threepid invite will be rejected.
  
          Note that if the threepid is already associated with a Matrix user ID, Synapse
          will call user_may_invite with said user ID instead.
  
          Args:
              inviter_userid: The user ID of the sender of the invitation
              medium: The 3PID's medium (e.g. "email")
              address: The 3PID's address (e.g. "alice@example.com")
              room_id: The room ID
  
          Returns:
              True if the user may send the invite, otherwise False
          """
          for callback in self._user_may_send_3pid_invite_callbacks:
              with Measure(
                  self.clock, "{}.{}".format(callback.__module__, callback.__qualname__)
              ):
                  may_send_3pid_invite = await delay_cancellation(
                      callback(inviter_userid, medium, address, room_id)
                  )
              if may_send_3pid_invite is False:
                  return False
  
          return True
  
      async def user_may_create_room(self, userid: str) -> bool:
          """Checks if a given user may create a room
  
          If this method returns false, the creation request will be rejected.
  
          Args:
              userid: The ID of the user attempting to create a room
  
          Returns:
              True if the user may create a room, otherwise False
          """
          for callback in self._user_may_create_room_callbacks:
              with Measure(
                  self.clock, "{}.{}".format(callback.__module__, callback.__qualname__)
              ):
                  may_create_room = await delay_cancellation(callback(userid))
              if may_create_room is False:
                  return False
  
          return True
  
      async def user_may_create_room_alias(
          self, userid: str, room_alias: RoomAlias
      ) -> bool:
          """Checks if a given user may create a room alias
  
          If this method returns false, the association request will be rejected.
  
          Args:
              userid: The ID of the user attempting to create a room alias
              room_alias: The alias to be created
  
          Returns:
              True if the user may create a room alias, otherwise False
          """
          for callback in self._user_may_create_room_alias_callbacks:
              with Measure(
                  self.clock, "{}.{}".format(callback.__module__, callback.__qualname__)
              ):
                  may_create_room_alias = await delay_cancellation(
                      callback(userid, room_alias)
                  )
              if may_create_room_alias is False:
                  return False
  
          return True
  
      async def user_may_publish_room(self, userid: str, room_id: str) -> bool:
          """Checks if a given user may publish a room to the directory
  
          If this method returns false, the publish request will be rejected.
  
          Args:
              userid: The user ID attempting to publish the room
              room_id: The ID of the room that would be published
  
          Returns:
              True if the user may publish the room, otherwise False
          """
          for callback in self._user_may_publish_room_callbacks:
              with Measure(
                  self.clock, "{}.{}".format(callback.__module__, callback.__qualname__)
              ):
                  may_publish_room = await delay_cancellation(callback(userid, room_id))
              if may_publish_room is False:
                  return False
  
          return True
  
      async def check_username_for_spam(self, user_profile: UserProfile) -> bool:
          """Checks if a user ID or display name are considered "spammy" by this server.
  
          If the server considers a username spammy, then it will not be included in
          user directory results.
  
          Args:
              user_profile: The user information to check, it contains the keys:
                  * user_id
                  * display_name
                  * avatar_url
  
          Returns:
              True if the user is spammy.
          """
          for callback in self._check_username_for_spam_callbacks:
              with Measure(
                  self.clock, "{}.{}".format(callback.__module__, callback.__qualname__)
              ):
                  # Make a copy of the user profile object to ensure the spam checker cannot
                  # modify it.
                  res = await delay_cancellation(callback(user_profile.copy()))
              if res:
                  return True
  
          return False
  
      async def check_registration_for_spam(
          self,
          email_threepid: Optional[dict],
          username: Optional[str],
          request_info: Collection[Tuple[str, str]],
          auth_provider_id: Optional[str] = None,
      ) -> RegistrationBehaviour:
          """Checks if we should allow the given registration request.
  
          Args:
              email_threepid: The email threepid used for registering, if any
              username: The request user name, if any
              request_info: List of tuples of user agent and IP that
                  were used during the registration process.
              auth_provider_id: The SSO IdP the user used, e.g "oidc", "saml",
                  "cas". If any. Note this does not include users registered
                  via a password provider.
  
          Returns:
              Enum for how the request should be handled
          """
  
          for callback in self._check_registration_for_spam_callbacks:
              with Measure(
                  self.clock, "{}.{}".format(callback.__module__, callback.__qualname__)
              ):
                  behaviour = await delay_cancellation(
                      callback(email_threepid, username, request_info, auth_provider_id)
                  )
              assert isinstance(behaviour, RegistrationBehaviour)
              if behaviour != RegistrationBehaviour.ALLOW:
                  return behaviour
  
          return RegistrationBehaviour.ALLOW
  
      async def check_media_file_for_spam(
          self, file_wrapper: ReadableFileWrapper, file_info: FileInfo
      ) -> bool:
          """Checks if a piece of newly uploaded media should be blocked.
  
          This will be called for local uploads, downloads of remote media, each
          thumbnail generated for those, and web pages/images used for URL
          previews.
  
          Note that care should be taken to not do blocking IO operations in the
          main thread. For example, to get the contents of a file a module
          should do::
  
              async def check_media_file_for_spam(
                  self, file: ReadableFileWrapper, file_info: FileInfo
              ) -> bool:
                  buffer = BytesIO()
                  await file.write_chunks_to(buffer.write)
  
                  if buffer.getvalue() == b"Hello World":
                      return True
  
                  return False
  
  
          Args:
              file: An object that allows reading the contents of the media.
              file_info: Metadata about the file.
  
          Returns:
              True if the media should be blocked or False if it should be
              allowed.
          """
  
          for callback in self._check_media_file_for_spam_callbacks:
              with Measure(
                  self.clock, "{}.{}".format(callback.__module__, callback.__qualname__)
              ):
                  spam = await delay_cancellation(callback(file_wrapper, file_info))
              if spam:
                  return True
  
          return False
  